1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device which is provided with a movable section to be operated on the basis of a displacement action of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device which is capable of detecting displacement of a movable section by the aid of a piezoelectric/electrostrictive element, and a method for producing the same. In particular, the present invention relates to a piezoelectric/electrostrictive device which is excellent in strength, shock resistance, and moisture resistance and which makes it possible to efficiently operate a movable section to a great extent, and a method for producing the same.
2. Description of the Related Art
Recently, a displacement element, which makes it possible to adjust optical path length and position on the order of submicrons, is required, for example, in the fields of optics, magnetic recording, and precision machining. Development is advanced for the displacement element based on the use of the displacement brought about by the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in FIG. 41, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixation section 204, a movable section 206, and a beam section 208 for supporting them which are formed in an integrated manner with a hole 202 provided through a plate-shaped member 200 composed of a piezoelectric/electrostrictive material and with an electrode layer 210 provided on the beam section 208 (see, for example, Japanese Laid-Open Patent Publication No. 10-136665).
The piezoelectric actuator is operated such that when a voltage is applied to the electrode layer 210, the beam section 208 makes expansion and contraction in a direction along a line obtained by connecting the fixation section 204 and the movable section 206 in accordance with the inverse piezoelectric effect or the electrostrictive effect. Therefore, the movable section 206 can perform circular arc-shaped displacement or rotational displacement in the plane of the plate-shaped member 200.
On the other hand, Japanese Laid-Open Patent Publication No. 63-64640 discloses a technique in relation. to an actuator based on the use of a bimorph. In this technique, electrodes for the bimorph are provided in a divided manner. The actuator is driven due to the selection of the divided electrodes, and thus the highly accurate positioning is performed at a high speed. This patent document (especially in FIG. 4) discloses a structure in which, for example, two bimorphs are used in an opposed manner.
However, the piezoelectric actuator described above involves such a problem that the amount of operation of the movable section 206 is small, because the displacement in the direction of expansion and contraction of the piezoelectric/electrostrictive material (i.e., in the in-plane direction of the plate-shaped member 200) is transmitted to the movable section 206.
All of the parts of the piezoelectric actuator are made of the piezoelectric/electrostrictive material which is a fragile material having a relatively heavy weight. Therefore, the following problems arise. That is, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Further, the piezoelectric actuator itself is heavy, and its operation tends to be affected by harmful vibrations (for example, residual vibration and noise vibration during high speed operation).
In order to solve the problems described above, it has been suggested that the hole 202 is filled with a filler material having flexibility. However, it is clear that the amount of displacement, which is brought about by the inverse piezoelectric effect or the electrostrictive effect, is decreased even when the filler material is used.
Further, the actuator described in Japanese Laid-Open Patent Publication No. 63-64640 has such a structure that the bimorph itself is composed of two piezoelectric elements which are laminated with each other, and the bimorph is stuck to a fixation member or a mediating member. Therefore, the stress tends to remain, resulting from, for example, the curing and the shrinkage of an adhesive and the heating treatment required for the sticking and the lamination. It is feared that the displacement action is disturbed by the internal residual stress, and it is impossible to realize the displacement and the resonance frequency as designed. Especially, when the actuator is small in size, the influence of the adhesive is increased.
Accordingly, a method is conceived in order to exclude the influence of the adhesive required to effect the sticking, in which the actuator is composed of, for example, an integrated sintered product made of ceramics to give a structure in which no adhesive is used. However, also in this case, it is inevitably feared that the internal residual stress arises due to the difference in behavior of thermal shrinkage between respective members during the sintering.
Further, when the actuator is small, a problem is involved such that the fixation property of the actuator and the attachment property of the actuator to another part are deficient.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a piezoelectric/electrostrictive device and a method for producing the same which make it possible to obtain a displacement element that is scarcely affected by harmful vibration and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance. This makes it possible to realize a light weight of the device, especially light weight in a movable section or a fixation section, and improve the handling performance of the device and the attachment performance for parts to be attached to the movable section or the fixation performance of the device, so that the movable section may be greatly displaced at a relatively low voltage. It is possible to achieve a high speed in the displacement action of the device, especially of the movable section (realization of a high resonance frequency), as well as a sensor element which makes it possible to accurately detect vibration of the movable section.
According to the present invention, there is provided a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections and a fixation section for supporting the thin plate sections; movable sections provided at forward end portions of the pair of thin plate sections; and one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; wherein any one of the movable sections and the fixation section has mutually opposing end surfaces; and a distance between the end surfaces is not less than a length of the movable section.
The movable section, the fixation section, and the thin plate section may be made of ceramics or metal. Alternatively, each of the components may be made of a ceramic material, or each of them may be made of a metal material. Further, each of the components may be constructed to have a hybrid structure obtained by combining those produced from materials of ceramics and metal.
It is also preferable that any one of the movable section and the fixation section is provided with a cutoff section; and a part of the cutoff section constitutes the mutually opposing end surfaces. It is also preferable that the thin plate section, the movable section, and the fixation section are composed of a ceramic substrate integrated into one unit by co-firing a ceramic green laminate and cutting off unnecessary portions. It is also preferable that the piezoelectric/electrostrictive element has a film-shaped configuration, and it is integrated with the ceramic substrate by means of sintering.
In this arrangement, the piezoelectric/electrostrictive element may have a piezoelectric/electrostrictive layer and a pair of electrodes formed on the piezoelectric/electrostrictive layer. It is also preferable that the piezoelectric/electrostrictive element has a piezoelectric/electrostrictive layer and a pair of electrodes formed on both sides of the piezoelectric/electrostrictive layer, and one electrode of the pair of electrodes is formed on at least the thin plate section. In this arrangement, the vibration caused by the piezoelectric/electrostrictive element can be efficiently transmitted via the thin plate section to the movable section or the fixation section. Thus, it is possible to improve the response performance. Especially, it is preferable that the piezoelectric/electrostrictive element is constructed in a stacked form comprising a plurality of units each including the piezoelectric/electrostrictive layer and the pair of electrodes.
When the arrangement as described above is adopted, the generated force of the piezoelectric/electrostrictive element is increased, and thus it is possible to obtain large displacement. Further, it is possible to obtain a high resonance frequency owing to the increase in rigidity of the device itself, making it easy to achieve the high speed of the displacement action.
It is also preferable that a gap is formed between the mutually opposing end surfaces. It is also preferable that a member which is the same as a constitutive member of any one of the movable section and the fixation section, or a plurality of members which are different therefrom are interposed between the mutually opposing end surfaces, the same member or the different members including, for example, glass, cement, and organic resin, preferably organic resin such as those based on epoxy, acrylic, polyimide, phenol, silicone, terpene, xylene, styrene, melamine, methacrylic, and rubber, or mixture or copolymer thereof. Especially, in view of, for example, the joining performance, the handling performance, and the hardness, it is preferable to allow organic resin or the like based on epoxy, acrylic, and methacrylic to intervene. In order to further enhance the hardness, it is also preferable to mix a filler such as an inorganic material.
Especially, it is possible to effectively realize a light weight of the movable section or the fixation section by forming the gap between the mutually opposing end surfaces, allowing the member lighter than the constitutive member of the movable section or the fixation section to intervene between the mutually opposing end surfaces, or joining the end surfaces with small one of the members described above. Accordingly, it is possible to increase the resonance frequency without decreasing the amount of displacement of the movable section or the fixation section.
When the gap is formed between the mutually opposing end surfaces, a part of the movable section or the fixation section including one end surface and another part of the movable section or the fixation section including the other end surface are more flexible, resulting in strong resistance to the deformation. Therefore, it is possible to obtain excellent handling performance of the piezoelectric/electrostrictive device.
Further, the distance between the end surfaces is not less than the length of the movable section. Therefore, the attachment area can be increased, when another part is attached to the movable section. Thus, it is possible to improve the attachment performance for the part. It is now assumed that the part is secured, for example, with an adhesive or the like. The part can be held by being interposed on the both sides. Thus, it is possible to reliably secure the part.
When the part is held by being interposed on the both sides, the height of the part and the height of the movable section are not simply added. Accordingly, it is possible to maintain the height of the whole including the part to be low. Further, the length of the movable section can be made smaller than the distance on the side of the end surface. Therefore, the physical property of an adhesive or the like for sticking or bonding the part effectively makes the action. Thus, it is possible to increase the displacement.
On the other hand, when the fixation section has the mutually opposing end surfaces, it is possible to strongly fix the piezoelectric/electrostrictive device according to this invention to a predetermined fixation portion. Thus, it is possible to improve the reliability.
As described above, according to the present invention, it is possible to obtain the displacement element which is scarcely affected by harmful vibration and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance, making it possible to realize a light weight of the device, especially a light weight of the movable section or the fixation section, and improve the handling performance of the device as well as the attachment performance for parts to be attached to the movable section, the miniaturization, and the fixation performance of the device, so that the movable section may be greatly displaced, and it is possible to achieve a high speed of the displacement action of the movable section (realization of a high resonance frequency), as well as the sensor element which makes it possible to accurately detect vibration of the movable section.
In the production of the piezoelectric/electrostrictive device, for example, when the piezoelectric/electrostrictive element is formed on a ceramic laminate (obtained by laminating ceramic green sheets followed by sintering into one unit), for example, by means of the lamination or the integrated sintering based on the use of the film formation method as described later on, the internal residual stress is generated at a portion to be formed into the piezoelectric/electrostrictive element and/or the thin plate section. Especially, when the piezoelectric/electrostrictive element is formed on the ceramic laminate by means of the integrated sintering, the internal residual stress tends to be generated at the portion to be converted into the piezoelectric/electrostrictive element and/or the thin plate section, due to the shrinkage and the difference in coefficient of thermal expansion of the constitutive members caused during the sintering.
If the piezoelectric/electrostrictive device is produced and used starting from this state, the movable section does not exhibit the desired displacement in some cases, even when a predetermined electric field is applied to the piezoelectric/electrostrictive layer for constructing the piezoelectric/electrostrictive element, because of the following reason. That is, the material characteristic of the piezoelectric/electrostrictive layer and the displacement action of the movable section are inhibited by the internal residual stress generated in the piezoelectric/electrostrictive element and/or the thin plate section.
In the present invention, the mutually opposing end surfaces are provided on any one of the movable section and the fixation section. Therefore, the distance between the end surfaces is, for example, shortened by the internal residual stress generated in the piezoelectric/electrostrictive element and/or the thin plate section. That is, the internal residual stress, which has been generated in the piezoelectric/electrostrictive element and/or the thin plate section, is released by the movement of the end surfaces.
Further, in the present invention, the distance between the end surfaces is made to be wide. Therefore, even when the distance between the end surfaces is narrowed due to the internal residual stress, it is possible to give a margin sufficient to attach another part between the end surfaces.
As described above, in the present invention, the displacement action of the movable section is not inhibited by the internal residual stress. It is possible to obtain the displacement action of the movable section as approximately designed and expected. Additionally, the release of the internal residual stress also makes it possible to improve the mechanical strength of the device.
When a hole is formed by both inner walls of the pair of thin plate sections, inner walls of the movable sections, inner walls of the plurality of members, and an inner wall of the fixation section, it is also preferable that the hole is filled with a gel material. In this arrangement, although the displacement action of the movable section is usually restricted due to the presence of the filler material, the invention described above intends to reduce the weight as a result of the formation of the end surfaces on the movable section or the fixation section, and increase the displacement amount of the movable section. Therefore, the restriction of the displacement action of the movable section by the filler material is counteracted, and it is possible to realize the effect owing to the presence of the filler material, i.e., the realization of the high resonance frequency and the maintenance of the rigidity.
According to another aspect of the present invention, there is provided a method for producing a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections and a fixation section for supporting the thin plate sections; movable sections provided at forward end portions of the pair of thin plate sections; and one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; the method comprising a step of forming the movable sections or the fixation section having mutually opposing end surfaces wherein a distance between the end surfaces is not less than a length of the movable section, by cutting off a predetermined part of any one of a portion to be formed into the movable sections or a portion to be formed into the fixation section after producing at least the piezoelectric/electrostrictive element on the thin plate section.
As a result, there is provided the movable section or the fixation section which has the mutually opposing end surfaces. Accordingly, the internal residual stress, which has been generated in the piezoelectric/electrostrictive element and/or the thin plate section during the production, is released, for example, by shortening the distance between the end surfaces. Therefore, the displacement action of the movable section is not inhibited by the internal residual stress.
The phrase xe2x80x9cafter producing the piezoelectric/electrostrictive elementxe2x80x9d referred to herein indicates a state in which at least the piezoelectric/electrostrictive layer is formed. As for the electrode to be formed after the formation of the piezoelectric/electrostrictive layer, the electrode may be formed after performing the cutoff to form the movable section or the fixation section having the mutually opposing end surfaces.
The provision of the movable section or the fixation section having the mutually opposing end surfaces realizes the light weight of the movable section or the fixation section. Therefore, the piezoelectric/electrostrictive device, which makes it possible to increase the resonance frequency, can be efficiently produced with ease without decreasing the amount of displacement of the movable section. Thus, it is possible to realize the mass production of the high performance piezoelectric/electrostrictive device.
Further, the movable section or the fixation section is bent more flexibly, and it is strongly resistant to deformation. Therefore, the piezoelectric/electrostrictive device is excellent in handling performance. Owing to the presence of the mutually opposing end surfaces and the wide distance between the end surfaces, when another part is attached to the movable section, it is possible to provide a large attachment area therefor. Thus, it is possible to improve the attachment performance for the part. When a part is interposed and bonded, it is possible to improve the displacement.
According to still another aspect of the present invention, there is provided a method for producing a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections and a fixation section for supporting the thin plate sections; movable sections provided at forward end portions of the pair of thin plate sections; and one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; the method comprising a step of producing a ceramic laminate by integrally sintering a ceramic green laminate including at least a ceramic green sheet having a window and ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic laminate; a step of forming the piezoelectric/electrostrictive element on an outer surface of a portion of the ceramic laminate to be formed into the thin plate section; and a cutoff step of forming the movable sections or the fixation section having at least mutually opposing end surfaces wherein a distance between the end surfaces is not less than a length of the movable section, by means of at least one time of cutoff treatment for the ceramic laminate formed with the piezoelectric/electrostrictive element.
Accordingly, in the production of the piezoelectric/electrostrictive device, especially when the piezoelectric/electrostrictive element is formed on the ceramic laminate by means of the sintering, the internal residual stress, which is generated in the piezoelectric/electrostrictive element and/or the thin plate section, can be effectively released. Therefore, when the piezoelectric/electrostrictive device is produced by using the ceramic green sheet-laminating method, it is possible to realize the light weight of the device, especially the light weight of the movable section or the fixation section, and improve the handling performance of the device, the attachment performance for parts to be attached to the movable section, and the fixation performance of the device. Thus, it is possible to allow the movable section to make large displacement.
It is also preferable that in the step of producing the ceramic laminate, the ceramic laminate is produced by integrally sintering a ceramic green laminate including a plurality of ceramic green sheets each having a window for forming the movable section or the fixation section having at least the mutually opposing end surfaces, and the ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic laminate; and in the cutoff step, the movable section or the fixation section, which has at least the mutually opposing end surfaces and in which the distance between the end surfaces is not less than the length of the movable section, is formed by means of the cutoff treatment for the ceramic laminate formed with the piezoelectric/electrostrictive element.
It is also preferable that in the step of producing the ceramic laminate, the ceramic laminate is produced by integrally sintering a ceramic green laminate including a plurality of ceramic green sheets each having a window for forming a portion to be formed into the movable section or a portion to be formed into the fixation section having at least the mutually opposing end surfaces partially connected to one another, and the ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic laminate. In the cutoff step, the portion to be formed into the movable section or the portion to be formed into the fixation section having at least the mutually opposing end surfaces partially connected to one another is formed by means of the cutoff treatment for the ceramic laminate formed with the piezoelectric/electrostrictive element, and the movable section or the fixation section, which has the mutually opposing end surfaces and in which the distance between the end surfaces is not less than the length of the movable section, is formed by cutting off the connecting portion.
It is also preferable that the production method further comprises a step of allowing a plurality of members different from a constitutive member of the movable section or the fixation section to intervene between the mutually opposing end surfaces. In this case, organic resin may be used as at least one member of the plurality of members.
Therefore, the piezoelectric/electrostrictive device and the method for producing the same according to the present invention can make the use of the active device including, for example, various transducers, various actuators, frequency region functional parts (filters), transformers, vibrators, resonators, oscillators, and discriminators for the communication and the power generation, as well as the sensor element for various sensors including, for example, ultrasonic sensors, acceleration sensors, angular velocity sensors, shock sensors, and mass sensors. Especially, the piezoelectric/electrostrictive device and the method for producing the same according to the present invention can be preferably utilized for various actuators to be used for the mechanism for adjusting the displacement and the positioning and for adjusting the angle for various precision parts such as those of optical instruments and precision mechanical equipments.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.